Modulation system



Dec. 27, 1927. 1,654,281

R. L. DAVIS MODULATION SYSTEM Filed Aug. 6, 1925 3 I t 5 ll WITNESSE I INVENTOR 4%,!4 gwmb RObQ/"f DO V1 3.

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RUBER'I 1L. DAVIEL 0F WILKINSBURG. PENNSYLVANIA, ASSIG-NOR T0 WESTINGHOUFSE ELEUTH-IC do MANUFAGTU'RING COMPANY, A CORPORATION OF PENNSYLVANIA.

MODULATION SYSTEM.

Application filed August My invention relates to radio signalling systems and particularly to modulation means therefor.

An object of my invention is to provide a radio sending system in which a larger current may be passed through the modulator triode than through the oscillator triode.

Another object of my invention is to provide a radio transmitting system with means between the oscillator and the modulator elements for the passage of a vibratory current, and for the transformation thereof from one potential toanother.

Another object of my invention is to provide an oscillation generator and a modu later therefor, which are separately connected to an energy source and with means whereby an audio-frequency current is conveyed .thereloetween.

Modulation of a triode oscillation generator has customarily been attained by the so-called constant current modulation sys-- tem shown in Patentztthllfldl? to Heising. 'l'he system shown in this patent is however restricted in its operation by the fact that the oscillator triode of such a system is limited in the range over which the current value therethrough can be changed without deviation from a proportionate change in voltage applied to the grid thereof. Likewise, the oscillation generator, because of the fact of its oscillation, takes less current at a given applied voltage than a similar modulator triode with a similar grid bias takes at the similar applied voltage. The current change through the modulator produces a change in voltage upon the oscillation generator which is less thanthat required to produce complete modulation, but the energy capacity of the modulator triode is suflicient to provide complete modulation.

ll ly invention provides transformer means having a ratio different than unity for the transfer of the oscillatory current component. Advantage is taken of the higher energy absorbing properties of the modulator triode to )rovide complete modulation of the oscillation generator without the necessity for exceeding the change in voltageupon the grid of the modulator at which a linear ratio of current change is obtained.

My invention further provides means for the convenient insertion of a meter which can be calibrated to indi ate the degree of completeness of modulation and means 6, 1925. Serial No. 43,434.

whereby the current fluctuation may be substantially compensated so that a small portion only is present in the supply circuit, or whereby the entire fluctuation may be passeil through the supply source.

Other objects and structural details of my invention will be apparent from the following description when read in connection with the accompanying drawings wherein:

Figure 1 is a diagrammatic representation of circuits and apparatus embodying a preferred form of my invention; and

Fig.2 is a diagrammatic representation of circuits and apparatus embodying another form.

In the system of my invention, an oscillation radiating means 1 is provided, and is connected to a. local oscillatory circuit 2 which is energized by a triode oscillation generator 3. A triode modulator t has its grid connected through a transformer to a microphone 6 and a local battery T. The cathodes of the triodes 3 and t are connected to a source of electric heating energy it. :t source ofplate current energy 9 has its negative terminal connected to the cathode circuit of the triodes 3 and 4:.

The positive terminal of the generator 9 is connected to the plates of the triodes 3 and 4 respectively, through the windings 11 and 12 of the transformers 14: and 15. The windings 16 and 17 of the transformer are connected through a meter 18. The connections between the windings 1t and 17 may be made directly, as shown in Fig. .l or reversed as shown in Fig. 2. An audio-frequency condenser 22 is connected across the generator 9 as shown in Fig. 2. A radio-frequency choke coil is connected in the oscillator plate lead, to prevent radio-frequency current reaching other parts of the system.

In the operation of my device, the filaments of the triodes 3 and t are energized by the generator 8. The plate circuits of these triodes are also energized from the generator 9 in the usual manner. Oscillations are produced by the triode 8 in any well known manner, The generator 9 supplies current to the oscillator 8 through the winding 11 of the transformer 14 and it also supplies current to the modulator t through the Winding 12 of the transformer 15. Upon the production of vibratory currents of the microphone 6, a vibratory potential is sup plied to the grid of the triode l, causing tlti vibratory changes in the plate current.

These vibratory currents induce corresponding vibratory currents in the winding 17 which traverse the winding 16 of the transformer 14 and through the 1netcr18.

The vibratory currents in the winding 16 induce a vibratory potential in the winding 11, which potential is impressed upon the triode 3 and causes changes in the plate current therethrough and thereby change in the amplitude of the oscillations generated by it.

The ratio between the windings 17 and 12, and the windings 16 and 11 is such that the combined efiect produces a transformation ratio that is different than unity and it may be such that a higher vibratory voltage. is generated in coil 11 thanoccurred in coil 12. This higher voltage causes a larger vibratory current through the triode 3 than if the modulator were directly connected to the oscillator and produces more nearly complete modulation of the oscillations.

In the embodiment shown in Fig. 1, in which the coils 17 and 16 are connected directly, a reduction in the current of the modulator 4 produces an increase in current in the oscillator 3. These currents'partially neutralize each other in the exterior supply circuit by current traversing the common junction point 19 and the conductor 21. A

minimum amount of vibratory current, depending upon the ratio of transformation between the respective transformers, traverses the current source 9.

In the embodiment shown in Fig. 2, the

' connections of the coils 17 and 14 are reversed by different voltages may be supplied to the respective triodes and if desired. triodes having different characteristics may be e111- bodied.

By the device of my invention, I am enabled to provide a radio sending system and modulating means therefor, which is capable of producing more nearly complete modulation without the introduction of distortion than can be produced by the apparatus of the prior art and I am also enabled to provide a system adapted to the employment of triodes having different characteristics and to operate them at different applied voltages.

While I have shosvn but two embodiments of my invention in the preceding description, it is capable of other modifications without departing from the spirit thereof, and it is desired, therefore, that only such limitations shall be imposed thereon as are required by the prior art, or indicated in the appended claims.

I claim as my invention:

1. A radio signalling system comprising a trio'de oscillation generator, a source of energy for the anode circuit thereof, a transformer having the secondary coil thereof connected between said generator and said source, a triode amplifier system, a second transformer having the primary winding thereof connected in the amplifier anode circuit, and connections from the secondary Winding of said second-mentioned transformer to the pr mary winding of said firstmentioned transIormer.

2. A radio signalling system comprising an oscillation generator, and an amplifier having supply circuits, a source of current for said generator and said amplifier, transformers in said supply circuits, and connections therebetween whereby current changes in said circuits occur simultaneously in the same direction.

In testimony whereof, I have hereunto subscribed my name this 11th day of July,

ROBERT L. DAVIS. 

